This invention relates to ultrasonic imaging systems and methods, and particularly to ultrasonic imaging systems and methods that utilize both harmonic and fundamental imaging modes.
Ultrasonic imaging systems that combine ultrasonic images from multiple transmit beams to form a single improved image are described for example in U.S. Pat. Nos. 5,568,813; 5,111,824; 5,462,057; and 5,579,770. The methods described in these patents however do not address the issue of providing high image quality in harmonic images of technically difficult examinations.
Hossack et al. U.S. patent application Ser. No. 08/904,825, assigned to the assignee of the present invention, discloses a method and system that combine nearfield harmonic imaging and farfield fundamental imaging to create a single improved image. This application also discloses a system and method that combine a nearfield image which is an amplitude matched combination of fundamental and harmonic signals with a farfield fundamental image to form a single improved image.
Danhua Zhao U.S. Pat. No. 5,897,500, assigned to the assignee of the present invention, discloses a method and system that combines nearfield fundamental imaging and middlefield or farfield imaging to create a single composite image. In one system and method, nearfield and farfield regions are modulated primarily as a function of fundamental mode image signals and a middlefield region is modulated primarily as a function of harmonic mode image signals.
In spite of the improvements provided in the above identified Hossack and Danhua Zhao applications, a need presently exists for an ultrasonic imaging system and method that provide improved lateral imaging, particularly for use in harmonic imaging systems used to image tissue without added contrast agent. In such cases, particularly in technically difficult examinations, the lateral performance may be less than optimum because of degradation of image signals along edge lines. For example, the signal to noise ratio decreases along edge lines for vector and sector scan formats.